Researcher seeks origin of scent

Clarkia breweri, an annual native to California, used by
Eran Pichersky in his research on scents in plants. Photo courtesy
Eran Pichersky

By Sally Pobojewski
News and Information Services

A rose by any other name may still smell like a rose, but new
research by a U-M biologist suggests a rose with different genes may
smell more like a banana.

Since 1990, Eran Pichersky, associate professor of biology, has
been identifying specific genes and enzymes that trigger production
of small organic molecules in plant cells called volatiles. When
these compounds evaporate off the surface of petals and stigma, they
produce a flower's scent. Each species of flower has a different
scent, because each produces its own unique combination of volatile
compounds.

So far, Pichersky has isolated four gene-enzyme combinations. One
catalyzes the major volatile compound found in many flowers and also
in oil of bergamot. The second smells like a cross between basil and
cloves, the third like wintergreen, and the fourth has a strong odor
of bananas.

The plant model Pichersky uses in his research is Clarkia,
an annual native to California. Of approximately 25 species in the
Clarkia genus, only one--Clarkia breweri--has an odor.
Except for its scent, C. breweri is virtually identical
genetically and morphologically to another species, C.
concinna.

"It appears that C. breweri has evolved from C.
concinna and so the scent of C. breweri is a recently
acquired trait," Pichersky says. "Our hypothesis is that new plant
species create new scent compounds simply by modifying the expression
of a few key genes."

Pichersky believes all flowering plants may contain at least some
of the genes responsible for floral scent. If he can figure out how
plants selectively "turn on" or express specific genes during their
developmental stage, scientists may one day use standard genetic
engineering techniques to enhance a flower's natural odor or create a
banana-scented rose. Pichersky's genes already are being used by
several commercial companies. These companies are inserting Clarkia's
scent genes into ornamental plants to create flowers with new scents
and into vegetables, such as tomatoes, to create fruits with new
aromas. Future plans call for inserting scent genes into certain crop
plants, so the flowers will attract more pollinating insects and the
plants will produce more seed.